Automatic tuning system



Oct. 28, 1952 c, a COLEMAN 2,616,066

AUTOMATIC TUNING SYSTEM Filed March 3, 1951 WITNESSES: INVENTOR (47%? Clarence B.Colemon.

9t;- 1 TTORNEY Patented Oct. 28, 1952 2,616,066 AUTOMATIC TUNING SYSTEM Clarence B. Coleman, Baltimore, Md., assignor t Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application March 3, 1951, Serial No. 213,709

7 Claims.

My invention relates to automatic tuning systems, and more particularly to a system for automatically tunin an electrical network to resonance.

Automatic tuning systems as exemplified by the prior art of which I am aware are subject to a number of disadvantages. Such tuning systems generally comprise an electrical network to be tuned to resonance, a motor mechanically coupled to a tuning element of the network, and means responsive to some electrical condition of the network for controlling the motor. Several systems of tuning are designed to stop the tuning motor at resonance by the maximizing of a voltage. Such arrangements provide poor tuning accuracy due to the inertia of the mechanical system. Even though the resonant condition may be anticipated, consistent tuning accuracy is made impossible because the detuning efiect of the over-shoot varies with frequency and ambient temperature. Most tuning systems of they amplitude type require an adjustment corresponding to the peak output at resonance. This necessitates provision of some means to automatically adjust sensitivity, since it is not usually possible to obtain exactly the same radio frequency output at resonance over a wide frequency range. Further, many tuning systems require complete scanning by the motor before the actual tuning cycle is started, resulting in low-speed tuning.

It is, accordingly, an object of my invention to provide an automatic tuning system which is simpler and more reliable than the automatic tuning systems of the prior art.

It is another object of my invention to provide animproved automatic tuning system which disturbs to a, minimum extent, the radio frequency circuits to which it is applied.

It is another object of my invention to provide an improved automatic tuning system which will require an extremely small amount of input power.

It is another object of my invention to provide an automatic tuning system in which the problem of over-shooting is obviated.

It is a further object of my invention to provide an improved automatic tuning system which will operate satisfactorily over a wide range of frequency outputs.

It is a further object of my invention to provide an improved automatic tuning system which will operate satisfactorily over a wide range of frequencies without necessity for adjustment.

It is a still further object of my invention to provide an improved automatic tuning. system in which the tuning is accomplished within a minimum period of time.

In accordance with my invention, a tuning element or elements of the network to be tuned are mechanically coupled to a tuning element adjusting mechanism, which may be a reversiblemotor. A secondary control circuit is provided for causing the adjusting mechanism to move the tuning element back and forth between its limits when no signal is applied to the network to be tuned. A pulse generating circuit is provided so that when a signal is applied to the network, a control pulse will be generated each time the network is tuned through resonance. The control pulse initiates operation of a primary control circuit. The primary control circuit comprises a memory device which establishes a parameter corresponding to the conditions for resonance at theinstant when the control pulse is generated. The primary control circuit further comprises comparison means for controlling the adjusting mechanism. Thus, when the network is tuned through resonance, the control pulse initiates operation of the primary control circuit to establish a parameter corresponding to the conditions for'resonance. Immediately thereafter, thecomparison means causes reversal of the adjusting mechanism, to tune the network back toward resonance. When the conditions for resonance are again present, as established by the memory device, the comparison means causes the adjusting mechanism to stop. The network is thus tuned to resonance. In a preferred embodiment of my invention where the comparison means comprises a pair of electronic discharge devices, a grid biasing arrangement is used which is such that the only net grid bias applied is that due to' the error voltage developed by over-shoot of the adjusting mechanism. This arrangement results in good sensitivity for the system.

My invention will be best understood and other objects and advantages thereof will appear from the following detailed description taken in connection with the accompanying drawing, in which:

Fig. l is a schematic diagram showing a preferred embodiment of my invention, and

Fig. 2 is a group of curves to facilitate explanation of the control pulse generating scheme.

Referring now to Fig. 1 of the drawing, there is shown a tunable network H comprising an inductance I3and -a capacitor I5 connected in parallel. The tuning element of the network is shown as the variable capacitor I5. A signal source I? is shown in block form as being connected across the input terminals of the tunable network H. The signal source may, of course, be a part of any equipment with which it is desired to associate the automatic tuning system of my invention. A pulse generating circuit I9 is shown connected across the terminals of the tunable network II so as to obtain a sample of the network voltage. The pulse generating network I9 comprises the primary winding of a coupling transformer 2I, a first resistor 23 and a first rectifier 25 connected serially with the input terminals of the pulse generator circuit I9. shunting the primary winding of the coupling transformer 2! is a second resistor 21 and a second rectifier 29 which is poled like the first rectifier. Also included in the pulse generating circuit is the coupling transformer secondary winding and a capacitor BI connected serially with the output terminals of the pulse generator t9, and a resistor 33 shunting said output terminals. The output of the pulse generator "circuit is connected to the input terminals of a suitable amplifier 35 shown as a block. One outcathode of a control tube having also an anode and a control electrode. The other output terminal of the amplifier is connected to the control electrode of said control tube II.

The tuning element I5 of the tunable network I I is mechanically coupled to the shaft of an adjusting device shown schematically as a reversible motor 43. Also coupled mechanically to the tuning element I5 and the shaft of the reversible motor 43 are the movable contacts 45, 41 of a pair of ganged potentiometers 49, 5I. These movable contacts are adjusted to besynchronous with each other and with the tuning element I5. The function of the potentiometers 49, 5| will be hereinafter more fully described. Power is supplied to the reversible motor 43 via first and second buses 53, 55 in the conventional manner from a source not shown. is utilized to control the rotation of the reversible motor '43. The center contact 59 of the balance relay '5! is connected to the second power sup ply bus 55 and the right and left contacts BI, 33

are connected to respective windings 65, :67 of the reversible motor 43. The center contact 59 is :biased to its neutral position by a pair of springs 39. The balance relay '5'! has a pair of energizing windings II., I3, and unbalanced currents in these windings will cause the center contact 59 to move from its normally neutral po- 'sition to close a circuit between one or the other of the motor windings 65, S! to the second power supply bus 55. The operation of the balance relay 5'! is controlled by a pair of electronic discharge devices I5, I! which may be designated for convenience as first and second comparison tubes 75. TI respectively. These tubes may be triodes of any suitable type. Positive and negative voltages may be obtained from a source shown schematically as a potentiometer "I9 having first and second movable contacts El, 83 and a center-point grounded at 85. The terminals of this potentiometer "I9 are connected to a source of direct current power not shown. Positi-ve anode potential is supplied to the comparison tubes 75, TI from-connections which may be traced from the second movable contact 83 of the potentiometer through respective first and second normally open contacts 87, 89 of a pri- A balance relay 51 mary control relay SH and respective balance relay energizing windings II, I3 to the anodes of the respective tubes. The ganged potentiometers 49, 5| are connected in parallel, one of their common terminals being connected to ground at 93 and the other common terminal being connected to the first movable contact 8| of the potentiometer I9. The movable contact of the upper ganged potentiometer 49 is connected to the grid of the second comparison tube "I1 and through first normally closed contacts 95 of a start relay 9'! to the grid of the first comparison tube I5. The movable contact 41 of the lower ganged potentiometer 5| is connected through a resistor 99 to the cathodes of the comparison tubes I5, 1?. Operating potential for the first control tube AI is established by a resistor IllI which is connected between the oathode of that tube M and the second movable contact 83 of the potentiometer 19. The anode of the first control tube 3| is connected through 'the energizing winding I33 of the start relay SI to the second movable contact 83 of the poten tiometer 79. The start relay 9'! is of the slow release type for a purpose to be hereinafter described. A circuit may be traced from the first power supply bus 53 through the normallyclosed contacts N35 of a reset relay I31, through the second normally open contacts I09 of the start relay '9'? and through the energizing winding I 'I'l cf the primary control relay 91 to the second powersupply bus 55. The second normally open contacts I 99 of the start relay -91 are s'hunted'by the third normally open contacts I I3 of the primary control relay 9I. The reset relay I Il is also of the slow release type fora purpose to be hereinafter explained. The energizing winding 1 I5 of the reset relay I0! is connected in series with a push-button H9 across the power supply buses 5'3, 55. A secondary control relay I'2I, of the self locking type, is also "provided. The functions of the various relays mentioned above will be understood from the explanation of the operation of the system, which appears below. "The secondary control relay I2I has a pair of back-to-back contacts I23, I25 which are connected respectively in shunt with the first and second normally open contacts 39, 81 of the primary control relay 9 I. The secondary controlre lay I2'I is shown schematically as having first and second energizing windings I21, I29. The armature I3I of the first energizing winding I21 operates the contacts I23, I25 of the relay. The armature I33 of the second energizing winding I29 operates a plunger I35 which is biased by a spring I3! toward a latch I39 which extends axially from the armature I3'I of the first energizing coil 21. When the first energizing coil I21 is energized, its armature is pulled up, closing the first contacts I25 and opening the second contacts IN. The relay I2I islocked in this position by the plunger latch mechanism I35, I39. The second energizing winding 529, when ener- 'gi'zed, trips the latch so that the second contact nal of each winding is connected through the normally open contacts of respective first-and second limit switches MI, M3, to the first power .supply bus 53. These limit switches I4I, I43 are operated by the movable contact 41 of the second ganged potentiometer 5|. A capacitor which serves as a memory device and which will be hereinafter termed the memory capacitor I45 is connected between the grid of the first comparison tube I5 and ground at I41.

I will now explain the manner of operation of the automatic tuning system of my invention. Let it be assumed for convenience that when the left contact 63 of the balance relay 5! is closed, the motor 43 will rotate to move the movable contacts of the ganged potentiometers 49, 5I toward ground. Further assume that no signal is supplied initially to the network II to be tuned, and that all relays are initially in the position shown. Under these conditions, the motor rotation is controlled by the secondary control relay I2I in cooperation with the limit switches I4I, I43. power is supplied to the system, theright energizing winding I3 of the balance relay 51 will be energized and the balance relay will close its right contact BI, and the motor 43 will begin to move-the movable contacts of the ganged 150- tentiometers 49, 5I in the direction away from ground 93. The motor will continue in this direction until the movable contact 4! of the lower ganged potentiometer 5| closes the upper limit switch I 4|. energizes the first winding I2! of the secondary control relay I2I to close its first contacts I25 and open its second contacts I23. The first winding II of the balance relay 5'! will now be energized to close its left contact 83. cause the motor 43 to reverse, and begin to move the movable contacts of the ganged potentiometers 49, 5I toward ground 93. When the movable contact 41 of the second ganged potentiometer 5| reaches its ground side limit, the

lower limit switch I43 will be closed. Closing of .the lower limit switch will energize the second winding I29 of the secondary control relay I2! to trip the latch and cause the second contacts I23 to close and the first contacts I25 to open. The motor 43 will again reverse, and begin to move the movable contacts of the ganged potentiometers 49, 5I away from ground 93. This operation will continue until a signal voltage is applied from the signal source IT to the tunable network I I. a I

When a signal is applied to the tunable network II, the potential at the terminals of the network will vary in magnitude, in the manner shown by curve a of Fig. 2, as the network is former 2| will vary as indicated by curve 0 of Fig. 2. The second rectifier 29 prevents negative voltage being applied to the transformer 2I. If the second rectifier were not employed, and it was attempted to amplify the waveform of curve b, Fig. 2, inaccuracy due to unsymmetrical clipping in the amplifier 35 might result. The waveform shown by curve 0 of Fig. 2 is peaked by the capacitor 3I, and the pulse input to the amplifier is as shown by curve d of Fig. 2. In the When operating Closing of the upper limit switch r This will curves of Fig. 2, the ordinates represent voltage, and the abscissas represent frequency.

Attention is now directed to the biasing arrangement for the comparison tubes I5, 11. Dual or ganged potentiometers 49, 5| are employed rather than a single potentiometer because of the limits on the voltage which may be applied to the grids of these tubes. In order to provide good sensitivity, the variation in voltage per unit of movement of the potentiometer movable contact must be high. This means that if the oathodes of the comparison tubes were grounded, it would be necessary to apply a large range of voltages to the grids as the potentiometer movable contact moved between its limits. The use lished in the grid circuits of the comparison tubes I5, II by means of the bias resistor conneoted between their cathodes and the movable contact 4'I of the lower ganged potentiometer 5|. This bias allows either comparison tube to conduct sufliciently to operate the balance relay when called upon to do so. The only voltage applied between the grids and cathodes of the comparison tubes other than the normal operating bias, is the error voltage developed by the over-shooting of the tuning motor 43. Looking, for example, at the first comparison tube I5, it will be noted that if the movable contact'45 of the upper ganged potentiometer 49 moves away from ground 93, the grid of that tube tends to become more negative. At the same time, however, the movable contact 41 of the lower ganged potentiometer 5I has moved away from ground by a like amount, with the tendency to make the cathode of the first comparison tube more negative with respect to ground. These ef fects cancel, leaving a net grid-cathode bias change of zero. Now the memory capacitor I45 in the grid circuit of the first comparison tube I5 will, so long as the start relay 9'! is deenergized, be charged to a voltage the magnitude of which is related to the position of the movable contacts 45, 41 of the ganged potentiometers 49, 5I at any given instant. This capacitor I 45 acts as a memory device. In other words, it remembers what the position of the movable contacts of the ganged potentiometers 49, 5I was at the instant when the start relay 9! was energized. When the start relay is energized, the

charging current supply for the memory capacitor is cut ofi, and a substantially fixed bias between the grid of the first comparison tube I5 and ground is established. From the instant of energization of the start relay 91, the cancelling effect of the ganged potentiometers 49, 5I on the grid-cathode bias is no longer effective with reference to the first comparison tube I5, but is still effective with respect to the second comparison tube 'I'I. With the foregoing explanation of the comparison tube biasing arrangement in mind, explanation of the operation I of the system as a whole, may proceed.

Let it be assumed that the movable contacts of the ganged potentiometers 49, 5| are moving away from ground as the tunable network .II is tuned through resonance. At the instant of resonance, a control pulse such as that shown .by curve cl of Fig. 2 is generated. This control pulse is amplified and applied to the grid of the control tube 4|. The control tube is rendered sufficiently conductive to operate the start relay 91 *to open 'its normally closed contacts 95 and close its normally open contacts l '9.

"The closing of the normally open contacts 7 l 89 'of'the start relayfi'l energizes the prim-ary'control relay 9L "The primary control relay *closes its third normally open contacts 1 F3 -to lock itself in-the energized-position. 'The-closing 'of the first and second normally open contacts 81, 89 of the primary control relay 9I renders operation of the secondary control relay l2! ineffective, -'=so -that the first and secondcompar'ison'tubes 15,11 =can=now conduct =simultaneously,'making it possible -forth e-' balanced relay center contact 59 to be moved to its neutral position, under proper conditions. Opening of the normally closed-contacts 95 of the start'relay 97 cuts off thesupply of charging current to the memory capacitor I45.

'Thememory capacitor M now establishes 'a substantially fixed 'gridto ground bias "for the first comparison tube 1'5 which corresponds to the po- *sition-of the variable capacitor l5-oi the tunable "network'l-l at the instant of resonance.

Nowas the variable capacitor is moved on through resonance, and the movable contacts of the gangedpotentiometers 69, 5| moveiurther away parison tube 15 more positive with respect to its cathode.

This tube will then deliver more current to the first-energizing winding H of the balance relay 5? and its'left .contact (53 will now be closed. The motor '43 .will thenreverse, caus- 'ing the variable capacitor IE .to be tuned back toward resonance, and the movable contacts of the ganged ,potentiometers &9, 5| .to move back toward ground .33. As the movable contact .41

.oithe. lower ganged potentiometer 5 I .moves back towardground, the.cathode-to-groundbias on the first-comparison tube 15 tendsto become more positive. The net grid-to cathodebias of the first comparison .tube .15 will then become more negative. When the bias on the first comparisontube reaches the original condition for resonance as established by the memory capacitor, the first and "second comparison tubes 15, l' 'l will-bacon- .ductingvequal amounts, and the'center contact of the balance -relay51 will be moved to its neutral position. iThus,ithermotor 43'will:b'estoppe'd with 1the=variablecapacitorl5 o'fthe tunable network I I in1th'e rexact position for resonance.

'As heretofore mentioned, the start relay 9'! is-ofthe-slow release type. This relayonce energized remains energized for a period of time su'flicient to'allow completion of the tuning cycle.

Suppose now'that the start relay 9'! has returned to its non-energized position'and that a signal of a di'fierent frequency is applied to the tunable network I l Under "these conditions, nothing happens-.zsince the primary-control relay 9| is still energized, andthe comparison tubes 15,11 continueto conduct equal amounts of current. To cause the system'tto-tune the'network H to the new frequency, the push button 1 I9 is operated,

energizing the reset'relay N37. The reset relay ithen iopens its contact [BE -causing the'primary *control relay 9! to be deenergized. The sec- -ondaryrcontrol relay i2| now takes over,and-a :new .ftuning cycle is accomplished in the same manner as was hereinbefore described. The-reset-relay IE1 is of the slow release type to insure that 'themotor lfi will attain the proper speed before the primary control :relay 9 I can rbe a ain -'servo-amplifier and a two-phase motor for'the balance relay and the motor shown. I desire, therefore, to be limited only insofar as is necessitated-by the prior art and the spirit of the-appended claims.

I claim asl'ny invention: 1. An automatic tuning system comprising :a primary circuit comprising-a network adap'tedfor connection to a source of oscillating energy and tunable to resonance at the -frequencyof said source, means connected to said networkior-producing a control pulse at the instant When-said network is tuned to resonance, a-secondary=ci1'- cu'it comprising means for tuning :said network through resonance, means to 'ooritrol saidituning means, including 'a memory device "actuable responsive to said control pulse for establishinga parameter corresponding 'to the condition I or resonance of saidnetwork, means connected in circuit with said memory device for reversing said tun'i-ngmeans and for stopping saidtuningmeans at'the instant when the condition of resonance, as established by said memory device, is again reached.

2. An automatic positioning system comprising an apparatus to "be positioned, =meansior moving saidapparatus through its range of positions, means for generating an electric control pulse at the instant when saidapparatus is in the desired position, a memory device 'actuable responsive to 'said control pulse for "establishing a parameter corresponding to the condition for the desired position of said apparatus, "means connected in circuit with said memory device "for reversing said first mentioned means and for stopping said first mentioned means at the instant when thecondition-for said desired position, as established by said memory device, is

again reached.

.nected .in circuit with said network forgenerating a controlpulse .when .said network is tuned to resonance, means responsive to said control pulsefor opening the grid bias supply circu'itto one of saiddischarge devices, and a'capac'itor connected in the grid circuit of said one dis- ;charge device to establish a substantially fixed bias component corresponding to thecondition of resonance-of said network.

6. An automatic tuning system comprising tunable network, tuning means "forsaid network,

"a reversible motor for adjusting said tuning means, first and second electronic'discharge devices, each having an anode, 'a 'cathodeand a control electrode, a balance relay having contacts for controlling the rotation of said motor and having an energizing coil connected in the anode circuit of each of said discharge devices, means for applying bias to said control electrodes, means for generating a control pulse when said network is tuned through resonance, means responsive to said control pulse for opening the control electrode bias supply to said first discharge device, and a capacitor connected in the grid circuit of said first discharge device to establish a substantially fixed bias component corresponding to the condition of resonance of said network.

'7. An automatic tuning system comprising a tunable network, tuning means for said network, a reversible motor, first and second electronic discharge devices each having an anode, a cathode, and a grid, a balance relay having contacts for controlling rotation of said motor, and having a pair of energizing coils, means connecting each said anode through a respective one of said energizing coils to a positive voltage source, first and second potentiometers connected in parallel, means connecting one common terminal of said potentiometer to a negative voltage source, means connecting the other common terminal of said potentiometers to ground, means connecting the movable contact of said first potentiometer to said grids, means connecting the movable contact of said second potentiometer to said cathodes, a capacitor connected between the grid of said first discharge device and ground, means mechanically coupling the movable contacts of said potentiometers and said tuning means to said motor, means for generating a control pulse when said network is tuned through resonance, and means responsive to said control pulse for opening the connection between the movable contact of said first potentiometer and the grid of said first discharge device.

CLARENCE B. COLEMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,300,742 Harrison et a1. Nov. 3, 1942 2,525,442 Bischoff Oct. 10, 1950 2,526,266 O'Brien Oct. 17, 1950 2,537,427 Seid et al. Jan. 9, 1951 

